Use for a +/- 38V 120w supply

[dimitrij]

Hi everybody
i have a 120W +/- 38V regulated power supply (measured without load) which i would like to use for a power amplifier.
Any suggestions about the amp to use with? i'm looking for something reasonably cheap to build (no gainclone, since i already have one...)
Can i use it to power a pass F3?

thanks a lot

[cbdb]

Originally Posted by dimitrij

Hi everybody
i have a 120W +/- 38V regulated power supply (measured without load) which i would like to use for a power amplifier.
Any suggestions about the amp to use with? i'm looking for something reasonably cheap to build (no gainclone, since i already have one...)
Can i use it to power a pass F3?

thanks a lot

First we need to know how much current it will supply. Is it 120w with the load across + and -. Or will it still put out 120w across + and ground. If its the first case this supply has too much voltage and not enough current for an audio amp. The main consideration is the 8 ohm load. At 32 volts it needs to source 4 amps. Class A amps usualy use lower voltage but higher current supplies than that. This supply looks like it will put out 2 amps at the very most or 32 watts into 8 ohms. This supply might build a 25 watt class AB amp.

[AndrewT]

hi,
if this is an SMPS then it will power a low wattage power amp badly.
It may power an preamp but the pre-amp must be designed to run at that voltage.

[dimitrij]

well, so far this power supply has been used with a single tda7294 chip (wich can deliver 100W), following the application note in the datasheet, so i guess it can be used for an audio amplifier...
120W it's the rating of the the toroidal tranformer. I don't know actually (but i will check) the current rating of the linear regulator. It is not a smps.

[Bigun]

I try to collect old power supplies for future amp building too ! - it would be good to know more about the psu you have.

If it's a linear power supply (big transformer and big capacitors) then you may want to rebuild it (replace old caps, add filtering, quieter rectifier etc.).

I'll assume you have a linear power supply.

I'll assume that the trafo is 120VA with two 25V a.c. secondaries (yes, a rather cavalier assumption). This gives you three options,

a) single pair of split rails +/-38V each capable of at least 2A, which when divided between L & R channels gives not very much. This is the last preferred option. If you have a transformer with only one secondary and no centre tap it's your only option though.

b) if you re-wire to create a single supply (you can do this so long as the transformer has two secondaries or a single centre-tapped secondary).
single rail supply +38V capable of at least 2A into each of L & R channel amplifier. This should allow you to build a Zen amplifier (F2?), you don't have to run it at the full 2A idle current, cut it down to around 1.4A.


c) if the trafo has two secondaries you can generate two pairs of split rails of roughly +/- 19V each capable of at least 2A

This option allows you to use a different secondary for the Left Channel and the Right channel should you want that kind of separation. You'll be flowing 2A through 8 Ohm speakers giving a +/-16V swing. My ignorant guess is that this would work best with a ClassAB amplifier which can get pretty close to the power supply rails. There are simple ClassAB amps you can build - look at Rod Elliot projects and Carlos' DX amp.


p.s. just saw your post - good, it's a linear supply !

[dimitrij]

thanks, i will check how my trafo is actually made.
later i will let you know which will be the destiny of this PSU!

[dimitrij]

I checked the trafo. it has two independent secondaries capable of providing 28 V ac each.
so i think i will go for option b. i will run some pspice simulation to see if i can use it for an
F2 amp wich runs at 1.4 a for each channel.
again, thank you very much!